The invention relates to a method for aligning color ink jet pens for an ink jet printer in order to provide improved quality and print resolution.
In multicolor ink jet printers, print quality is a function of accurate droplet placement on a print media. Incorrect droplet placement for a particular pixel location may be caused by the physical location of the nozzles of a pen as a result of pen alignment relative to another color pen or by differences in the drop flight time between different color pens. Regardless of the cause of the misalignment problems, alignment of the pens is critical to providing improved print quality.
Various means have been used to align pens. For example, the horizontal and vertical print alignment of two pens in an ink jet printer may be accomplished by delaying or advancing the ink droplet ejection from one of the pens. For vertical alignment, the delay/advance of ink droplet ejection is in the print passes while for horizontal alignment, the delay/advance of ink droplet ejection is in drop placement within a single print pass. However, for a printer containing three or more pens, alignment processes become much more difficult, particularly for increased print resolution. When three pens in a printer are operated simultaneously, conventional methods for advancing or delaying ink droplet ejection from the pens may not be able to provide a desired print resolution. A further alignment complication is introduced when the printer also contains a separate black ink jet pen. Misalignment of the ink droplets from the black and color ink jet pens greatly reduces the print quality provided by such an ink jet printer.
U.S. Pat. No. 4,878,063 to Katerberg describes a method for detecting misalignment and correcting register of color separation planes on a print medium. The color planes of the cyan, magenta and yellow color components of an image are said to be adjusted relative to the color plane of a black component of the image. According to the ""063 patent, lines of a first color printing subsystem are printed in an array of M parallel lines which are uniformly spaced N spaces from a base registration line located in the center of the array of parallel lines. A second array of M parallel lines of a second color printing subsystem are printed so that they are uniformly spaced apart N+1 spaces from a base registration line located in the center of the second array of parallel lines. The second array of parallel lines is said to be predeterminedly juxtaposed with respect to the first array of parallel lines in order to determine when the base registration marks of the first and second arrays are aligned. After visually inspecting the marks of the two arrays, a user selects the adjacent line mark pair of the juxtaposed arrays which are in the best alignment and this selection is stored in the printer memory. The stored data is said to be used to adjust the relative column print positions of the print heads by appropriate increments of adjustment steps. In the foregoing described method, the printhead is moved in both swath directions relative to a center position to provide the reference line arrays.
Despite the abundance of methods for color pen alignment, there continues to be a need for improved methods for aligning pens for multi-color ink jet printers in order to provide improved print resolution.
With regard to the foregoing, the invention provides a method for aligning multiple color ink jet pens to provide ink droplet placement within {fraction (1/600)} inch of desired droplet location. The method includes providing an ink jet printer containing a printhead carriage for retaining a black ink printhead and a multi-color ink printhead thereon. The black ink printhead contains a black ink pen and the color ink printhead preferably contains at least two pens for providing ink droplets on a print media.
According to the method, the carriage is first set to an initial first position with respect to a first swath direction across a print media. The carriage is then moved across the print media in the first swath direction with respect to the initial first position. As the carriage is moved across the print media, ink droplets are deposited from a first color ink pen to provide a series of first vertical line segments across a width of the print media, each of the first vertical line segments being spaced a first constant separation distance from a previously printed first vertical line segment. Ink droplets are also deposited on the print media from a second color ink pen to provide a series of second vertical line segments across the print media, each of the second vertical line segments being spaced a second constant separation distance from a previously printed second vertical line segment. A combination of the first and second series of vertical line segments provides a first alignment pattern.
The carriage is then reset to the initial first position with respect to the first swath direction across the print media. As the carriage is again moved across the print media in the first swath direction, ink droplets are deposited from the first color ink pen to provide a series of third vertical line segments across a width of the print media, each of the third vertical line segments being spaced a first constant separation distance from a previously printed third vertical line segment. The carriage is then optionally reset to an initial second position with respect to the first swath direction across the print media. As the carriage is moved across the print media in the first direction from the initial second position, ink droplets from the black ink pen are deposited on the print media to provide a series of fourth vertical line segments across the print media, each of the fourth vertical line segments being spaced a fourth constant separation distance from a previously printed fourth vertical line segment. The combination of third and fourth series of vertical line segments provides a second alignment pattern.
The vertical line segments of the first alignment pattern are then visually inspected and a set of line segments which are in substantial horizontal alignment with one another is selected. Likewise, a set of line segments from the second alignment pattern which are in substantial horizontal alignment with one another is selected and the selected line segments are provided to a substantially permanent printer memory location.
In another aspect the invention provides a method for aligning multiple color ink jet printheads to provide ink droplet placement within {fraction (1/600)} inch of desired droplet location. The method includes providing an ink jet printer containing a printhead carriage for retaining a black ink printhead and a multi-color ink printhead thereon, the black ink printhead containing a black ink pen and the color ink printhead containing at least two pens for providing ink droplets on a print media. The carriage is set to an initial first position with respect to a first swath direction across a print media. As the carriage is moved across the print media in the first swath direction with respect to the initial first position, ink droplets are deposited from a first ink pen to provide a series of first vertical line segments across a width of the print media, each of the first vertical line segments being spaced a first constant separation distance from a previously printed first vertical line segment.
The carriage is then set to an initial second position with respect to a second swath direction opposite the first swath direction across a print media. As the carriage is moved across the print media in the second swath direction with respect to the initial second position, ink droplets are deposited from a black ink pen to provide a series of second vertical line segments across the print media, each of the second vertical line segments being spaced a second constant separation distance from a previously printed second vertical line segment. The combination of first and second series of vertical line segments provides a first alignment pattern.
The carriage is again reset to the initial first position with respect to the first swath direction across the print media. As the carriage is moved across the print media in the first swath direction with respect to the initial first position, ink droplets are deposited from a second ink pen other than black to provide a series of third vertical line segments across a width of the print media, each of the third vertical line segments being spaced a first constant separation distance from a previously printed third vertical line segment.
The carriage is then set to the initial second position with respect to the second swath direction opposite the first swath direction across the print media, and is moved across the print media in the second direction from the initial second position, while depositing ink droplets from the black ink pen to provide a series of fourth vertical line segments across the print media, each of the fourth vertical line segments being spaced a fourth constant separation distance from a previously printed fourth vertical line segment. The combination of third and fourth series of vertical line segments provides a second alignment pattern. For higher resolution printing, it is preferred to provide the second and fourth vertical line segments using two passes of the black ink pen across the print media.
After printing the line segments, the line segments of the first alignment pattern are visually inspected and a set of line segments which are in substantial horizontal alignment with one another is selected. Likewise, a set of line segments of the second alignment pattern which are in substantial horizontal alignment with one another is selected. The selected set of line segments are then provided to a printer memory location.
A feature of the invention is that individual pen alignment is based on a reference color other than black except when printing with black ink only. Accordingly, print resolution may be adapted to provide ink droplets within {fraction (1/600)} of an inch and/or {fraction (1/1200)} of an inch of the desired droplet location. In contrast, when black is selected as a reference color for pen alignment the alignment error factor has been found to be two to three times the error factor obtained from use of a reference color other than black.